Question 1196844
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"4 times as slow" is common (but sloppy) everyday English; but it is poor mathematical form....<br>
I will assume it means that it takes Rachel 4 times as long as Monica to do the work.<br>
That means when working together Rachel does 1/4 as much work as Monica; and that means she does 1/5 of the work.  (If you don't see that right away, look at it like this: Rachel does 1/5 of the work; Monica does 4 times as much work, which is 4/5 of the work; together they do 1/5 of the work plus 4/5 of the work, which is the whole job.)<br>
So in 3.5 hours Rachel does 1/5 of the work; that means the amount of time it would take her to do the job alone is 5*3.5 = 17.5 hours.<br>
ANSWER: 17.5 hours<br>